Pilot-Scale Experimental Investigation on Dry Capture of Mercury and SO₃ in Smelting Gas of Acid Making

In this study, a novel dry capture process utilizing a mixed adsorbent of ZnO and CuS was proposed for the simultaneous removal of Hg⁰ and SO₃ in flue gas from zinc smelting, addressing severe mercury pollution and high SO₃ concentrations. The experimental results showed that flue gas cooling caused the SO₃ to transform into sulfuric acid mist, which changed the reaction mechanism from a gas-solid to a liquid-solid reaction and helped to improve the SO₃ removal efficiency. Additionally, properly increasing the absorbent/SO₃ molar ratio significantly improved the SO₃ removal performance. However, excessive absorbent injection could cause aggregation and uneven dispersion of the absorbent particles in the flue gas, therefore impairing the effectiveness of SO₃ capture. Under typical operating conditions (flue gas flow rate of 3500 m³/h, flue gas temperature of 180 °C, ZnO/SO₃ molar ratio of 0.74, and residence time of 0.5 s), using a mixed absorbent of ZnO and CuS achieved an SO₃ removal efficiency of up to 32.6%, and a total mercury capture at 43.2%, of which the Hg⁰ removal attained a remarkable 76.3%. These results preliminarily confirm the feasibility of the dry capture technology for simultaneous removal of SO₃ and mercury, laying the foundation for further application and promotion.